Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), is a global health problem. Treatment of drug-susceptible TB involves months of therapy with multiple potentially toxic antibiotics. Treatment of TB has become even more difficult by the emergence and increasing prevalence of multi-drug resistant M.tb. This proposal focuses on the development of a novel therapy that targets M.tb iron (Fe) acquisition, a process that is critical to its ability to cause disease. Ga(NO3)3 is a FDA- approved drug for treating hypercalcemia of malignancy. It interferes with cellular Fe metabolism by competing with Fe for uptake/use. We find that Ga also decreases M.tb Fe acquisition, inhibits growth of both drug-susceptible and drug-resistant M.tb strains growing in vitro extracellularly and within human macrophages. Ga also demonstrated efficacy in murine models of M.tb infection. Intermittent systemic delivery of Ga(NO3)3 for a few days has shown minimal toxicity in humans. However, treatment of TB would likely require more sustained treatment regimens. Ways to improve targeting of Ga to infected macrophages, extend dosing intervals, or avoid systemic administration would improve Ga's therapeutic index. There have been considerable advances in recent years in the aerosol delivery of drugs to the lung, as well as cellular targeting of nanoparticles to accomplish these goals. Therefore, we hypothesize that Ga delivery by aerosol or nanoparticle to the lung could prove to be novel, well-tolerated, and effective therapies for TB that would work via disruption of M.tb Fe metabolism. In order to test the above hypothesis we propose to accomplish the following specific aims: 1. Identify forms of Ga that exhibit maximal in vitro potency against extracellular and intracellular M.tb, including MDR- and XDR-TB, with the goal of arriving at lead compounds. 2. Develop formulations of two lead Ga compounds that will allow them to be administered by inhalation for the treatment of pulmonary TB and determine their biodistribution, pharmacokinetics, toxicity and efficacy in murine models of pulmonary TB. 3. Develop nanoparticle formulations of two lead Ga compounds that will allow them to be administered for the treatment of pulmonary TB and determine their biodistribution, pharmacokinetics, toxicity and efficacy in murine models of pulmonary TB. 4. Determine mechanisms of action of the lead Ga formulations against M.tb, potential for emergence of resistance, and effect of the presence of other TB drugs on Ga anti-mycobacterial activity. RESEARCH DESIGN AND METHODOLOGY: Human monocyte-derived macrophages and murine models of TB will be employed along with fully virulent strains of M.tb. The work will emphasize: Fe and Ga acquisition by M.tb: Ga biodistribution, pharmacokinetics, toxicity; and potential bacterial target for Ga antimicrobial activity. Experimental methods employed include: development of Ga formulations suitable for aerosol or nanoparticle-mediated delivery; bacterial uptake of radiolabeled Fe and Ga, growth of M.tb in vitro and in vivo, murine models of pulmonary TB, quantitation of Ga in tissues. POTENTIAL IMPACT ON VETERAN HEALTH CARE: Veterans are at high risk for pulmonary TB. This work could lead to development of novel treatments for TB that would benefit veterans.